The present invention relates generally to modular integrated rail systems for combat weapons. More specifically, the present invention relates to a unique dampening structure incorporated into an upper hand guard portion of a rail system in a manner that dampens shock waves and the resulting harmonic vibration caused by operation of the firearm.
As the field of combat and commercial weaponry expands, numerous add-on enhancements have become available for attachment to standard firearms, thereby significantly upgrading the capability of the firearm. Of particular interest in the area of combat weapons are the well-known M16/M4 weapon systems (M16 and M4 are trademarks of Colt Defense, Inc.), the FNH™ SCAR≯ weapon system (FN and SCAR are trademarks of FN Herstal, S.A.), and the Barrett≯ family of high caliber sniper weapons (Barrett is a trademark of Barrett Firearms Mfg., Inc.). However, the concepts of the present invention are equally applicable to all firearms, weapon systems, and add-on enhancements. In particular, the concepts of the present invention are most applicable to larger caliber service weapons such as the 50 caliber Barrett≯ M82A1 rifle. For purposes of illustration only, we refer to FIG. 1, which shows an image of the M82A1 rifle generally indicated at 10. The weapon 10 generally includes a receiver 12, stock 14, and barrel 16.
Most modern combat weapons further include a mil-std 1913 dovetail rail 18 extending along the top of the receiver. This integrated receiver rail provides a convenient mounting point for many types of enhancement devices such as scopes 20 and/or other sighting devices. The increasing development and refinement of laser sights, infrared lighting, visible lighting, night vision, and specialized scopes and magnifiers, and other accessories continues to drive the need for versatile and reliable integration systems that can support this important equipment and yet stand the test of rugged military use and abuse.
One of the issues of mounting sensitive electro-optic components on a weapon is that shock waves and harmonic vibration resulting from operation of the weapon are transmitted through the weapon and mounts into the mounted component. Shock waves and the resultant harmonic vibrations that travel through the mechanical structures of the weapon will fatigue, damage or destroy almost any electro-optical device over time. While some of the sighting devices that are employed with a firearm may be able to endure the shocks, many more are damaged and ultimately fail as a result of the transferred shock waves and harmonic vibration. All branches of the military are reporting increased instances of field failure of these expensive, highly sensitive optic components on all types of weapons. However, failures are particularly distinguished on the more powerful, higher caliber weapons.
Before proceeding, we will need to distinguish “recoil” from “shock waves” and “vibration”. Simply put, “recoil” is the backward push of a firearm. According to Newton's third law of motion, for every action there is an equal and opposite reaction. Recoil is thus an equal but opposite reaction of the weapon to the forward momentum of the projectile exiting the barrel. The expanding gas of the burning powder causes recoil. It forces the bullet out of the case and down the barrel and exerts an equal force back against the rear of the chamber. The force is the same in both directions.
Modern autoloading (automatic or semi-automatic) weapons have the same measured recoil as bolt action weapons, but the “kick” felt by the shooter is less for some types of actions. The spring systems that are used to cycle the weapon and load the next cartridge operate to distribute some of the recoil thrust that would be felt by the shooter.
In addition to recoil, every weapon also experiences higher frequency shock waves and harmonic vibration caused by slamming of the moving parts of weapon against each other. Webster's dictionary defines a “wave” as a disturbance that transfers energy progressively from point to point in a medium and may take the form of an elastic deformation of the medium. For purposes of this invention, the most important part of this definition is that a wave is a “disturbance” which travels through a medium. The medium through which the wave travels may experience local oscillation as the wave passes. Vibration refers to mechanical oscillations about an equilibrium point. Vibration is occasionally desirable, such as the motion of a tuning fork. More often, vibration is undesirable, wasting energy and creating unwanted disturbances. Free vibration occurs when a mechanical system is set off with an initial input (wave) and then allowed to vibrate freely. The mechanical system will then vibrate at its natural frequency and gradually damp down to zero. The simplest analogy is the ringing vibration of a piece of metal when struck by a hammer.
Referring now to FIG. 2, a set of 3 graphs depicts the magnitude of shock waves experienced by an M82A1 (50 caliber) sniper rifle firing a single round. Each graph represents a measurement along a liner axis with the x-axis extending lengthwise along the weapon, the y-axis extending transversely across the weapon, and the z-axis extending vertically through the weapon. Each graph is set out with acceleration on the y-axis and time and on the x-axis. There are three distinct events that generate shock waves in this semi-automatic weapon. First, the discharge of the cartridge creates an initial shock wave (event 1) 22. Second, the gas blow-back slams the bolt backward against the buffer spring, bottoming out against the bottom of the spring cavity (event 2) 24. Finally, the buffer spring sends the bolt forwardly slamming it into the rear end of the barrel to seat another round in the chamber (event 3) 26.
While existing buffer spring systems are intended to capture the energy of the rearward thrust of the bolt, they are not designed to dampen higher frequency shock waves and harmonic vibrations, which are distinctly different from recoil.
The prior art uncovered by the Applicant seeks to address the effects of recoil on scope mounts. Typically, these systems introduce a spring element that sits between the mount body and the rings and allows cushioned movement of the rings (and scope) longitudinally relative to the mount body.
U.S. Pat. No. 2,510,289 to Livermore discloses such a mounting system wherein a spring tube is positioned between the bases of the rings and the mount body to provide a cushioned buffer against recoil.
U.S. Pat. No. 2,710,453 to Beverly discloses another such mounting system where a compression spring is seated between a fixed pin and a movable pin to both allow the scope to be swung to one side and to be removed from the base.
U.S. Pat. No. 6,678,988 to Poff discloses yet another such mount where a lower rail portion is fixedly mounted on the weapon and an upper rail portion slidably moves relative to the lower rail portion, A scope is mounted on the upper rail. A pair of compression springs cushion forward and rearward movement of the upper rail relative to the lower rail caused by recoil. French patent FR2588370 is very similar to Poff in many respects.
U.S. Pat. No. 7,013,593 to Pettersson is directed to a holder device including springs that reduce axial recoil motion.
The Applicant's own U.S. Pat. No. 4,845,871 is cited for its disclosure of a pair of Belleville springs that are situated between a cam foot and a base to hold the mount in place. These springs are not intended to absorb recoil shock. However, they do provide a softer, cushioned interface between the hard mount and attachment rail of the weapon.
While each of the devices of the prior art is generally effective for its intended purpose, i.e. absorbing recoil thrust, none are directed at the unique problem of absorbing high frequency shock waves and harmonic vibration, which can destroy sensitive electro-optic  devices.